JP5907070B2 - Non-aqueous electrolyte for lithium battery or lithium ion capacitor and electrochemical device using the same - Google Patents

Description

  The present invention relates to a nonaqueous electrolytic solution capable of improving electrochemical characteristics in a wide temperature range and an electrochemical element using the same.

In recent years, electrochemical devices, particularly lithium secondary batteries, have been widely used for small electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage. Since these electronic devices and automobiles may be used in a wide temperature range such as a high temperature in midsummer or a low temperature of extremely cold, it is required to improve electrochemical characteristics in a wide range of temperatures.
In particular, in order to prevent global warming, there is an urgent need to reduce CO ₂ emissions, and hybrid electric vehicles are among the environmentally friendly vehicles equipped with power storage devices composed of electrochemical elements such as lithium secondary batteries and capacitors. (HEV), plug-in hybrid electric vehicles (PHEV), and battery electric vehicles (BEV) are required to spread quickly. However, automobiles have a long travel distance, and may be used in a wide temperature range from extremely hot areas in the tropics to extremely cold areas. Therefore, these on-vehicle electrochemical elements are required to have no deterioration in electrochemical characteristics even when used in a wide temperature range from high temperature to low temperature.
In the present specification, the term lithium secondary battery is used as a concept including so-called lithium ion secondary batteries.

The lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of occluding and releasing lithium, a non-aqueous electrolyte composed of a lithium salt and a non-aqueous solvent, and the non-aqueous solvent includes ethylene carbonate (EC), Carbonates such as propylene carbonate (PC) are used.
In addition, as the negative electrode, metal lithium, metal compounds that can occlude and release lithium (metal simple substance, oxide, alloy with lithium, etc.) and carbon materials are known, and in particular, lithium can be occluded and released. Lithium secondary batteries using carbon materials such as coke, artificial graphite and natural graphite have been widely put into practical use.

For example, a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite as a negative electrode material is a decomposition product generated by reductive decomposition of a solvent in a non-aqueous electrolyte on the negative electrode surface during charging. It has been found that the gas interferes with the desired electrochemical reaction of the battery, resulting in poor cycle characteristics. Moreover, when the decomposition product of the nonaqueous solvent accumulates, it becomes impossible to smoothly occlude and release lithium into the negative electrode, and the electrochemical characteristics in a wide temperature range are liable to deteriorate.
Furthermore, lithium secondary batteries using lithium metal, alloys thereof, simple metals such as tin or silicon, and oxides as negative electrode materials have high initial capacities, but fine powders progress during the cycle. In comparison, it is known that reductive decomposition of a non-aqueous solvent occurs at an accelerated rate, and battery performance such as battery capacity and cycle characteristics is greatly reduced. In addition, if these anode materials are pulverized or a decomposition product of a nonaqueous solvent accumulates, lithium cannot be smoothly inserted into and released from the anode, and the electrochemical characteristics in a wide temperature range are likely to be deteriorated.
On the other hand, a lithium secondary battery using, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO _4, or the like as the positive electrode includes a positive electrode material, a non-aqueous electrolyte, and a non-aqueous solvent in a non-aqueous electrolyte in a charged state. It has been found that degradation products and gases generated by partial oxidative decomposition locally at the interface of the battery inhibit the desired electrochemical reaction of the battery, resulting in degradation of electrochemical characteristics over a wide temperature range. Yes.

As described above, the battery performance has been deteriorated due to the movement of lithium ions or the expansion of the battery due to the decomposition product or gas when the non-aqueous electrolyte is decomposed on the positive electrode or the negative electrode. In spite of such a situation, electronic devices equipped with lithium secondary batteries are becoming more and more multifunctional and power consumption is increasing. As a result, the capacity of lithium secondary batteries has been increasing, and the volume occupied by non-aqueous electrolyte in the battery has become smaller, such as increasing the electrode density and reducing the useless space volume in the battery. . Therefore, the electrochemical characteristics in a wide temperature range are likely to be deteriorated by a slight decomposition of the nonaqueous electrolytic solution.
Patent Document 1 proposes a non-aqueous electrolyte containing a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound. For example, 2-methylglutaronitrile: ethylene It is suggested that an electrolytic solution in which a lithium salt is dissolved in a mixed solvent of carbonate: dimethyl carbonate = 50: 25: 25 (volume ratio) has a wide potential window.
Patent Document 2 and Patent Document 3 disclose that a lithium secondary battery using a nonaqueous electrolytic solution containing fluoroethylene carbonate and succinonitrile can improve safety against thermal shock.

JP 2010-165653 A International Publication No. 2007/081169 Pamphlet International Publication No. 2007/094625 Pamphlet

  An object of the present invention is to provide a nonaqueous electrolytic solution capable of improving electrochemical characteristics in a wide temperature range and an electrochemical element using the same.

The present inventors have examined in detail the performance of the above-described prior art non-aqueous electrolyte. As a result, the non-aqueous electrolyte of the above-mentioned patent document cannot be said to be sufficiently satisfactory for the problem of improving electrochemical characteristics in a wide temperature range such as low temperature discharge characteristics after high temperature storage. It was a fact.
Therefore, the inventors of the present invention have made extensive studies in order to solve the above problems, and in a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, two nitrile groups are connected in the non-aqueous electrolyte solution. A branched dinitrile compound having a main chain of an alkylene chain of 2 to 4 carbon atoms is contained in an amount of 0.001 to 5% by mass, and a cyclic carbonate having a specific amount of fluorine atoms or a specific amount of two nitrile groups are connected. The present inventors have found that when a linear dinitrile compound having an alkylene chain having 2 to 6 carbon atoms is combined, the electrochemical characteristics in a wide temperature range, particularly the electrochemical characteristics of a lithium battery can be improved.

That is, the present invention provides the following (1) to ( 8 ).
(1) In a non-aqueous electrolytic solution in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous solvent contains 0.1 to 30% by volume of a cyclic carbonate having a fluorine atom. A non-aqueous battery for lithium batteries or lithium ion capacitors, comprising a branched dinitrile compound having a main chain of an alkylene chain connecting nitrile groups having 2 to 4 carbon atoms in a proportion of 0.001 to 5% by mass Electrolytic solution.

(2) A branched dinitrile in which a main chain of an alkylene chain connecting two nitrile groups in the nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent has 2 to 4 carbon atoms 0.001 to 5% by mass of the compound and 0.001 to 5% by mass of a linear dinitrile compound in which an alkylene chain connecting two nitrile groups has 2 to 6 carbon atoms Non-aqueous electrolyte for lithium battery or lithium ion capacitor .

(3) In a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous solvent contains 0.1 to 30% by volume of a cyclic carbonate having a fluorine atom. 0.001 to 5% by mass of a branched dinitrile compound in which the main chain of the alkylene chain connecting the nitrile group has 2 to 4 carbon atoms, and the alkylene chain connecting the two nitrile groups has 2 to 6 carbon atoms A non-aqueous electrolyte for a lithium battery or a lithium ion capacitor, containing 0.001 to 5% by mass of a linear dinitrile compound.

(4) As the linear dinitrile compound, the number of carbon atoms of the alkylene chain connecting the two nitrile groups constituting the linear dinitrile compound is different from the number of carbon atoms of the main chain of the alkylene chain of the branched dinitrile compound. A non-aqueous electrolyte for a lithium battery or a lithium ion capacitor as described in (2) or (3) above, wherein

(5) In the branched dinitrile compound, at least one hydrogen atom of the main alkylene chain is substituted with an alkyl group having 1 to 2 carbon atoms. The nonaqueous electrolytic solution for a lithium battery or a lithium ion capacitor according to any one of 1).

(6) In the branched dinitrile compound, only one hydrogen atom bonded to the α-position carbon of one of the nitrile groups is substituted with a methyl group. A nonaqueous electrolytic solution for a lithium battery or a lithium ion capacitor as described in 5).
(7) The branched dinitrile compound is 2-methylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2-ethyl-3-methylsuccinonitrile, 2,2,3-trimethylsuccinonitrile, 2- Methyl glutaronitrile, 2,4-dimethyl glutaronitrile, 2-ethyl-4-methyl glutaronitrile, 2,2,4-trimethyl glutaronitrile, 2,3-dimethyl glutaronitrile, 2,3,4 -Trimethylglutaronitrile, 2-methyladiponitrile, 2,5-dimethyladiponitrile, 2-ethyl-5-methyladiponitrile, 2,2,5-trimethyladiponitrile, 2,3-dimethyladionitrile At least one selected from ponitrile, 2,4-dimethyladiponitrile, and 2,3,5-trimethyladiponitrile Non-aqueous electrolyte for a lithium battery or a lithium ion capacitor according to serial (5).

( 8 ) In an electrochemical device which is a lithium battery or a lithium ion capacitor provided with a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent, the nonaqueous electrolytic solution is the above (1) to ( 7 An electrochemical element, which is a nonaqueous electrolytic solution for a lithium battery or a lithium ion capacitor described in any one of 1).

  ADVANTAGE OF THE INVENTION According to this invention, electrochemical elements, such as a non-aqueous electrolyte which can improve the electrochemical characteristics in a wide temperature range, especially the low temperature discharge characteristic after high temperature storage, and a lithium battery using the same can be provided.

  The present invention relates to a non-aqueous electrolyte and an electrochemical device using the same.

[Non-aqueous electrolyte]
The non-aqueous electrolyte solution of the present invention is a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and the main chain of an alkylene chain linking a specific amount of two nitrile groups in the non-aqueous electrolyte solution has a carbon number. The branched chain dinitrile compound which is 2 or more and 4 or less is contained in an amount of 0.001 to 5% by mass, and the cyclic carbonate having a specific amount of fluorine atoms or the alkylene chain connecting the specific amount of two nitrile groups has 2 or more carbon atoms A non-aqueous electrolyte characterized by using a combination of 6 or less linear dinitrile compounds.

The reason why the nonaqueous electrolytic solution of the present invention can greatly improve the electrochemical characteristics in a wide temperature range is not necessarily clear, but is considered as follows.
The branched dinitrile compound in which the main chain of the alkylene chain connecting the two nitrile groups contained in the non-aqueous electrolyte of the present invention has 2 or more and 4 or less carbon atoms contains at least one hydrogen atom of the main alkylene chain. Since the alkyl group to be substituted becomes a steric hindrance, it is considered that a coating that suppresses oxidative decomposition of the electrolytic solution is formed by reacting slowly at the active sites on the positive electrode surface during the initial charge.
Furthermore, a compound such as a cyclic carbonate having a fluorine atom or a linear dinitrile compound in which an alkylene chain linking two nitrile groups has 2 to 6 carbon atoms, that is, the main chain of the alkylene chain linking two nitrile groups is carbon. When a compound having a specific electron-withdrawing group having a different structure from a branched dinitrile compound having a number of 2 or more and 4 or less is combined, the main chain of the alkylene chain connecting two nitrile groups is carbon number By forming a film in combination with a branched dinitrile compound that is 2 or more and 4 or less, the Li ion permeability of the formed film is improved and the effect of suppressing the oxidative decomposition of the electrolyte is further enhanced. It was found that the electrochemical properties in a wide temperature range from low temperature to high temperature have a specific effect that is remarkably improved.

  In the nonaqueous electrolytic solution of the present invention, the content of the branched dinitrile compound in which the main chain of the alkylene chain connecting two nitrile groups contained in the nonaqueous electrolytic solution has 2 to 4 carbon atoms is 0.001-5 mass% is preferable in a liquid. When the content is 5% by mass or less, a film is excessively formed on the electrode, and there is little risk of deterioration of electrochemical characteristics in a wide temperature range. When the content is 0.001% by mass or more, the film is formed. It is sufficient, and the effect of improving the electrochemical characteristics over a wide temperature range is enhanced. The content is preferably 0.05% by mass or more, and more preferably 0.2% by mass or more in the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 3% by mass or less, and more preferably 2% by mass or less.

As the branched dinitrile compound in which the main chain of the alkylene chain linking two nitrile groups has 2 to 4 carbon atoms, at least one hydrogen atom of the alkylene chain of the main chain is an alkyl group having 1 to 4 carbon atoms. The substituted one is more preferable, and the one in which at least one hydrogen atom of the main alkylene chain is substituted with an alkyl group having 1 to 2 carbon atoms is further preferable.
Specifically, 2-methylsuccinonitrile, 2-ethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2-ethyl-3-methylsuccinonitrile, 2,3-diethylsuccinonitrile, 2, 2-dimethylsuccinonitrile, 2,2,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2-methylglutaronitrile, 2-ethylglutaronitrile, 2,4- Dimethyl glutaronitrile, 2-ethyl-4-methyl glutaronitrile, 2,4-diethyl glutaronitrile, 2,2-dimethyl glutaronitrile, 2,2,4-trimethyl glutaronitrile, 2,2,4 , 4-tetramethylglutaronitrile, 2,3-dimethylglutaronitrile, 2,3,4-trimethylglutaronitrile, 3-methylg Talonitrile, 3,3-dimethylglutonitrile, 2-methyladiponitrile, 2-ethyladiponitrile, 2,5-dimethyladiponitrile, 2-ethyl-5-methyladiponitrile, 2,5-diethyl Adiponitrile, 2,2-dimethyladiponitrile, 2,2,5-trimethyladiponitrile, 2,2,5,5-tetramethyladiponitrile, 2,3-dimethyladiponitrile, 2,4 Preferred examples include -dimethyladiponitrile, 2,3,5-trimethyladiponitrile, 3-methyladiponitrile, and 3,3-dimethyladiponitrile.
Among these, when only one H of the α-position carbon (CH ₂ ) of one nitrile group is a methyl group, it is preferable because the effect of improving electrochemical characteristics in a wide temperature range is enhanced. -Methylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2-ethyl-3-methylsuccinonitrile, 2,2,3-trimethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglu Talonitrile, 2-ethyl-4-methylglutaronitrile, 2,2,4-trimethylglutaronitrile, 2,3-dimethylglutaronitrile, 2,3,4-trimethylglutaronitrile, 2-methyladipo Nitrile, 2,5-dimethyladiponitrile, 2-ethyl-5-methyladiponitrile, 2,2,5-trimethyladiponitrile, 2,3-dimethyl Ruadiponitrile, 2,4-dimethyladiponitrile and 2,3,5-trimethyladiponitrile are preferred. Furthermore, when the α-position carbon (CH ₂ ) of the other nitrile group is unsubstituted, the reactivity of the two nitrile groups is different, so that a film is formed without excessive densification, and the Li ion permeability is further improved. From such a viewpoint, 2-methylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2-methyladiponitrile, 2,3-dimethyladiponitrile, 2, 4-dimethyladiponitrile is particularly preferred.

In the nonaqueous electrolytic solution of the present invention, the volume ratio of the cyclic carbonate having a fluorine atom in the nonaqueous solvent is preferably 0.1% by volume or more, more preferably 1% by volume or more, particularly preferably 3% by volume. In addition, the upper limit is preferably 30% by volume or less, more preferably 25% by volume or less, and particularly preferably 20% by volume or less.
The cyclic carbonate having a fluorine atom includes 4-fluoro-1,3-dioxolan-2-one (FEC), trans or cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter, both are generically named) And at least one selected from “DFEC”, and particularly preferably FEC.

  In the nonaqueous electrolytic solution of the present invention, the content of the linear dinitrile compound in which the alkylene chain connecting two nitrile groups contained in the nonaqueous electrolytic solution has 2 to 6 carbon atoms is 0.001 to 5% by mass is preferable. When the content is 5% by mass or less, a film is excessively formed on the electrode, and there is little risk of deterioration of electrochemical characteristics in a wide temperature range. When the content is 0.001% by mass or more, the film is formed. It is sufficient, and the effect of improving the electrochemical characteristics over a wide temperature range is enhanced. The content is preferably 0.05% by mass or more, and more preferably 0.2% by mass or more in the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 3% by mass or less, and more preferably 2% by mass or less.

  In the nonaqueous electrolytic solution of the present invention, the branched dinitrile compound in which the main chain of the alkylene chain connecting two nitrile groups has 2 or more and 4 or less carbon atoms and the alkylene chain connecting two nitrile groups has 2 or more and 6 carbon atoms. When the linear dinitrile compound which is the following is used in combination, the branched dinitrile compound in which the main chain of the alkylene chain connecting the two nitrile groups has 2 to 4 carbon atoms and the alkylene chain connecting the two nitrile groups has the carbon number As total content of the linear dinitrile compound which is 2-6, 0.01-7 mass% is preferable in a non-aqueous electrolyte. If the content is 7% by mass or less, a film is excessively formed on the electrode, and there is little risk of deterioration of electrochemical characteristics in a wide temperature range. It is sufficient, and the effect of improving the electrochemical characteristics over a wide temperature range is enhanced. The content is preferably 0.1% by mass or more, and more preferably 0.3% by mass or more in the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 3.5% by mass or less.

  Further, a branched dinitrile compound in which the main chain of an alkylene chain connecting two nitrile groups has 2 to 4 carbon atoms and a linear dinitrile compound in which an alkylene chain connecting two nitrile groups has 2 to 6 carbon atoms In combination, the alkylene chain linking the two nitrile groups connects the two nitrile groups to the branched dinitrile compound content in which the main chain of the alkylene chain linking the two nitrile groups has 2 to 4 carbon atoms. When the mass ratio of the linear dinitrile compound content is 0.01 to 0.96, it is preferable because the effect of improving electrochemical characteristics in a wide temperature range is enhanced, and 0.2 to 0.8 is more preferable. .

  Further, a branched dinitrile compound in which the main chain of the alkylene chain connecting two nitrile groups has 2 to 4 carbon atoms and a linear dinitrile compound in which the alkylene chain connecting two nitrile groups has 2 to 6 carbon atoms In combination, a branched dinitrile compound in which the main chain of an alkylene chain connecting two nitrile groups has 2 to 4 carbon atoms and an alkylene chain connecting two nitrile groups has a carbon number of 2 to 6 carbon atoms. Two nitrile groups are linked to the content of a branched dinitrile compound in which the total content of the chain dinitrile compound is in the above range and the main chain of the alkylene chain linking the two nitrile groups has 2 to 4 carbon atoms When the mass ratio of the content of the linear dinitrile compound in which the alkylene chain has 2 or more and 6 or less carbon atoms is within the above range, electrochemical characteristics in a wider temperature range can be obtained. Preferably to above.

Specific examples of the linear dinitrile compound in which the alkylene chain connecting two nitrile groups has 2 or more and 6 or less carbon atoms include succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, and suberonitrile.
Among these, when combined with a compound having 4 or more carbon atoms in the alkylene chain connecting two nitrile groups, the effect of suppressing the oxidative decomposition of the electrolyte is further improved, so that the electrochemical property is improved over a wide temperature range. Therefore, adiponitrile, pimelonitrile, and suberonitrile are more preferable.

  In addition, a branched dinitrile compound in which the main chain of an alkylene chain connecting two nitrile groups has 2 to 4 carbon atoms and a linear dinitrile in which an alkylene chain connecting two nitrile groups has 2 to 6 carbon atoms When a compound is used in combination, the number of carbon atoms in the alkylene chain connecting the two nitrile groups constituting the compound as a linear dinitrile compound in which the alkylene chain connecting the two nitrile groups has 2 to 6 carbon atoms However, if the main chain of the alkylene chain linking the two nitrile groups has a carbon number of 2 or more and 4 or less, the number of carbon atoms of the main chain of the alkylene chain of the branched dinitrile compound may be different. Since the effect which suppresses decomposition | disassembly improves further, it is preferable.

  In the non-aqueous electrolyte solution of the present invention, by combining the non-aqueous solvent, electrolyte salt, and other additives described below, the effect of synergistically improving the electrochemical characteristics in a wide temperature range is exhibited.

[Nonaqueous solvent]
Examples of the non-aqueous solvent used in the non-aqueous electrolyte of the present invention include cyclic carbonates, chain esters, lactones, ethers, amides, phosphate esters, sulfones, mononitriles, S═O bond-containing compounds, and the like. It is preferable that both a cyclic carbonate and a chain ester are included.
The term chain ester is used as a concept including chain carbonate and chain carboxylic acid ester.

  Examples of the cyclic carbonate other than the cyclic carbonate having a fluorine atom include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, vinylene carbonate (VC), and vinyl ethylene carbonate (VEC). ) Etc. are mentioned suitably.

When the non-aqueous solvent contains ethylene carbonate and / or propylene carbonate, the resistance of the film formed on the electrode is reduced, and the content of ethylene carbonate and / or propylene carbonate is preferably 3 in the total volume of the non-aqueous solvent. Volume% or more, more preferably 5% by volume or more, particularly preferably 7% by volume or more, and the upper limit is 45% by volume or less, more preferably 35% by volume or less, and particularly preferably 25% by volume or less.
In addition, it is preferable that the non-aqueous solvent contains a cyclic carbonate having a carbon-carbon double bond, since electrochemical characteristics in a wide temperature range are further improved. As the cyclic carbonate having a carbon-carbon double bond, VC and VEC are more preferable, and VC is particularly preferable.
The content of the cyclic carbonate having a carbon-carbon double bond is 0.001% by volume or more, more preferably 0.1% by volume or more, particularly preferably 0.3% by volume, based on the total volume of the nonaqueous solvent. In addition, the upper limit is 5% by volume or less, more preferably 4% by volume or less, and particularly preferably 3% by volume or less.
The total content of the cyclic carbonate including the cyclic carbonate having a fluorine atom and the cyclic carbonate other than the cyclic carbonate having a fluorine atom is used in the range of 10% by volume to 40% by volume with respect to the total volume of the nonaqueous solvent. Is preferred. If the content is 10% by volume or more, the electrical conductivity of the non-aqueous electrolyte does not decrease and the electrochemical characteristics in a wide temperature range do not deteriorate. If the content is 40% by volume or less, the non-aqueous electrolyte The above-mentioned range is preferable because the viscosity of the resin does not increase and the electrochemical characteristics in a wide temperature range are not likely to deteriorate.
These cyclic carbonates may be used alone, and when two or more types are used in combination, the electrochemical properties in a wide temperature range are further improved, and three or more types are particularly preferable. Preferred combinations of these cyclic carbonates include EC and PC, EC and VC, PC and VC, VC and FEC, EC and FEC, PC and FEC, VEC and FEC, FEC and DFEC, EC and DFEC, PC and DFEC , VC and DFEC, VEC and DFEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and VEC, PC and VC and FEC, EC and VC and DFEC, PC and VC and DFEC EC, PC, VC, FEC, EC, PC, VC, DFEC and the like are preferable. Of the above combinations, the two types of combinations are preferably EC and VC, EC and FEC, PC and FEC, VC and FEC, etc., and the combination of three or more types is EC and PC and VC and EC. Combinations of PC and FEC, EC and VC and FEC, PC and VC and FEC, EC and PC, VC and FEC, and the like are preferable.

Examples of chain esters include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), and diethyl carbonate ( DEC), symmetric chain carbonates such as dipropyl carbonate and dibutyl carbonate, and chain carboxylic acid esters such as methyl propionate, ethyl propionate, methyl acetate, and ethyl acetate.
The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. If the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte is lowered and electrochemical characteristics in a wide temperature range. The above range is preferable because there is little risk of decrease.
Among the chain esters, chain esters containing a methyl group selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, and ethyl acetate are preferable, particularly methyl A chain carbonate having a group is preferred.
In the case of using a chain carbonate, it is more preferable that both a symmetric chain carbonate and an asymmetric chain carbonate are contained, and it is more preferable that the content of the symmetric chain carbonate is more than that of the asymmetric chain carbonate.
The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, and more preferably 55% by volume or more. As an upper limit, 95 volume% or less is more preferable, and it is still more preferable in it being 85 volume% or less. It is particularly preferred that dimethyl carbonate or diethyl carbonate is included as the symmetrical chain carbonate.
The asymmetric chain carbonate preferably has a methyl group, and methyl ethyl carbonate is particularly preferable.
The above case is preferable because electrochemical characteristics in a wider temperature range are improved.

  The ratio of the cyclic carbonate to the chain ester is preferably 10:90 to 45:55, and 15:85 to 40:55, from the viewpoint of improving the electrochemical properties in a wide temperature range. 60 is more preferable, and 20:80 to 35:65 is particularly preferable.

  Other non-aqueous solvents include tertiary carboxylic acid esters such as methyl pivalate, butyl pivalate, hexyl pivalate, octyl pivalate, oxalate esters such as dimethyl oxalate, ethyl methyl oxalate, diethyl oxalate, Tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, cyclic ethers such as 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxy Chain ethers such as ethane, amides such as dimethylformamide, phosphate esters such as trimethyl phosphate, tributyl phosphate, trioctyl phosphate, sulfones such as sulfolane, γ-butyrolactone, γ-valerolactone, α-angelica lactone, etc. Lactone, acetonitrile, propionitrile Mononitriles, sultone compounds such as 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, ethylene sulfite, hexahydrobenzo [1,3,2] dioxathiolane-2-oxide (1,2 -Cyclohexanediol cyclic sulfite), cyclic sulfite compounds such as 5-vinyl-hexahydro 1,3,2-benzodioxathiol-2-oxide, 2-propynyl methanesulfonate, methylenemethane disulfonate, etc. S = O bond-containing compound selected from sulfonic acid ester compounds, vinylsulfone compounds such as divinylsulfone, 1,2-bis (vinylsulfonyl) ethane, bis (2-vinylsulfonylethyl) ether, acetic anhydride, propionic anhydride A chain carboxylic anhydride such as Cyclic acid anhydrides such as hydrosuccinic acid, maleic anhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionic anhydride, methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotri Cyclic phosphazene compounds such as phosphazene and ethoxyheptafluorocyclotetraphosphazene, cyclohexylbenzene, fluorocyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), Aromatic compounds having a branched alkyl group such as tert-butylbenzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, biphenyl, ter Phenyl (o-, m-, p-form), diphenyl ether, fluorobenzene, difluorobenzene (o-, m-, p-form), anisole, 2,4-difluoroanisole, terphenyl partial hydride (1, Preferred examples include aromatic compounds such as 2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl).

  The above non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. The combinations include, for example, a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate, a chain carbonate and a lactone, a combination of a cyclic carbonate, a chain carbonate and an ether, a cyclic carbonate, a chain carbonate and a chain ester. And a combination thereof.

[Electrolyte salt]
Preferred examples of the electrolyte salt used in the present invention include the following lithium salts and onium salts.

(Lithium salt)
Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso -C ₃ F ₇ ) and other lithium salts containing a chain-like fluorinated alkyl group, and cyclic fluorides such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi An oxalate complex such as a lithium salt having an alkylene chain, lithium bis [oxalate-O, O ′] lithium borate or lithium difluoro [oxalate-O, O ′] lithium borate Lithium salt is preferably exemplified that. Among these, at least one selected from LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ is preferable, and LiPF _6, LiBF ₄ and LiN (SO ₂ CF _3). ) At least one selected from ₂ is more preferable.

(Onium salt)
Moreover, as an onium salt, the various salts which combined the onium cation and anion shown below are mentioned suitably.
Specific examples of the onium cation include tetramethylammonium cation, ethyltrimethylammonium cation, diethyldimethylammonium cation, triethylmethylammonium cation, tetraethylammonium cation, N, N-dimethylpyrrolidinium cation, N-ethyl-N-methylpyrrole. Dinium cation, N, N-diethylpyrrolidinium cation, spiro- (N, N ′)-bipyrrolidinium cation, N, N′-dimethylimidazolinium cation, N-ethyl-N′-methylimidazoli Preferable examples include nium cation, N, N′-diethylimidazolinium cation, N, N′-dimethylimidazolium cation, N-ethyl-N′-methylimidazolium cation, and N, N′-diethylimidazolium cation. Is The
Specific examples of the anion include PF ₆ anion, BF ₄ anion, ClO ₄ anion, AsF ₆ anion, CF ₃ SO ₃ anion, N (CF ₃ SO ₂ ) ₂ anion, N (C ₂ F ₅ SO ₂ ) ₂ anion. , Etc. are mentioned suitably.

  These electrolyte salts can be used singly or in combination of two or more.

  The concentration used by dissolving all the electrolyte salts is usually preferably 0.3 M or more, more preferably 0.7 M or more, and even more preferably 1.1 M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

[Production of non-aqueous electrolyte]
In the nonaqueous electrolytic solution of the present invention, for example, the main chain of an alkylene chain in which the above nonaqueous solvent is mixed and two nitrile groups are connected to the above electrolyte salt and the nonaqueous electrolytic solution is 2 carbon atoms. It can be obtained by adding a branched dinitrile compound having 4 or less or a straight chain dinitrile compound in which an alkylene chain connecting two nitrile groups has 2 to 6 carbon atoms.
At this time, it is preferable that the compound added to the non-aqueous solvent and the non-aqueous electrolyte to be used is one that is purified in advance and has as few impurities as possible within a range that does not significantly reduce the productivity.

  The non-aqueous electrolyte of the present invention can be used in the following first to fourth electrochemical elements, and as the non-aqueous electrolyte, not only a liquid but also a gelled one can be used. Furthermore, the non-aqueous electrolyte of the present invention can be used for a solid polymer electrolyte. Among them, the nonaqueous electrolytic solution of the present invention is used for the first electrochemical element (that is, for a lithium battery) or the fourth electrochemical element (that is, for a lithium ion capacitor) that uses a lithium salt as an electrolyte salt. It is preferably used, more preferably used for a lithium battery, and most preferably used for a lithium secondary battery.

[First electrochemical element (lithium battery)]
The lithium battery of the present invention is a generic term for a lithium primary battery and a lithium secondary battery. In this specification, the term lithium secondary battery is used as a concept including a so-called lithium ion secondary battery. The lithium battery of the present invention comprises the nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent. Components other than the non-aqueous electrolyte, such as a positive electrode and a negative electrode, can be used without particular limitation.
For example, as the positive electrode active material for a lithium secondary battery, a composite metal oxide with lithium containing one or more selected from cobalt, manganese, and nickel is used. These positive electrode active materials can be used singly or in combination of two or more.
Examples of such a lithium composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3. Examples thereof include Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , and LiCo _0.98 Mg _0.02 O ₂ . Moreover, LiCoO ₂ and LiMn ₂ O _4, LiCoO ₂ and LiNiO _2, may be used in combination as LiMn ₂ O ₄ and LiNiO _2.

In addition, in order to improve safety and cycle characteristics during overcharge, and to enable use at a charging potential of 4.3 V or higher with respect to Li, a part of the lithium composite metal oxide is replaced with another element. May be. For example, a part of cobalt, manganese, nickel is replaced with at least one element such as Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La, etc. , A part of O may be substituted with S or F, or a compound containing these other elements may be coated.
Among these, lithium composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ that can be used at a charged potential of the positive electrode in a fully charged state of 4.3 V or more on the basis of Li are preferable, and LiCo _1-x M _x O ₂ (where M is at least one element selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, 0.001 ≦ x ≦ 0.05) , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , Li ₂ MnO ₃ and LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe) More preferred is a lithium composite metal oxide that can be used at 4.4 V or higher on the basis of Li, such as a solid solution. When a lithium composite metal oxide that operates at a high charging voltage is used, the electrochemical characteristics in a wide temperature range are likely to be deteriorated due to a reaction with the electrolyte during charging, but in the lithium secondary battery according to the present invention, these A decrease in electrochemical characteristics can be suppressed.
In particular, in the case of a positive electrode containing Mn, the resistance of the battery tends to increase with the elution of Mn ions from the positive electrode, so that the electrochemical characteristics in a wide temperature range tend to be lowered. Lithium secondary batteries are preferred because they can suppress a decrease in these electrochemical characteristics.

Furthermore, lithium-containing olivine-type phosphate can also be used as the positive electrode active material. In particular, a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel and manganese is preferable. Specific examples thereof include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO _{4 and the} like.
Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and some of iron, cobalt, nickel, and manganese are replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb. , Cu, Zn, Mo, Ca, Sr, W and Zr can be substituted with one or more elements selected from these, or can be coated with a compound or carbon material containing these other elements. Among these, LiFePO ₄ or LiMnPO ₄ is preferable.
Moreover, lithium containing olivine type | mold phosphate can also be mixed with the said positive electrode active material, for example, and can be used.

As the positive electrode for lithium primary _{battery, CuO, Cu 2 O, Ag} 2 O, Ag 2 CrO 4, CuS, CuSO 4, TiO 2, TiS 2, SiO 2, SnO, V 2 O 5, V 6 O 12 , VO _x , Nb ₂ O ₅ , Bi ₂ O ₃ , Bi ₂ Pb ₂ O ₅ , Sb ₂ O ₃ , CrO ₃ , Cr ₂ O ₃ , MoO ₃ , WO ₃ , SeO ₂ , MnO ₂ , Mn ₂ O ₃ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO and other oxides of one or more metal elements or chalcogen compounds, sulfur such as SO ₂ and SOCl ₂ Examples thereof include compounds, and fluorocarbons (fluorinated graphite) represented by the general formula (CF _x ) _n . Among these, MnO ₂ , V ₂ O ₅ , graphite fluoride and the like are preferable.

When the pH of the supernatant liquid when 10.0 g of the positive electrode active material is dispersed in 100 ml of distilled water is 10.0 to 12.5, the effect of improving the electrochemical characteristics in a wider temperature range can be easily obtained. The case of 10.5 to 12.0 is more preferable.
Further, when Ni is contained as an element in the positive electrode, impurities such as LiOH in the positive electrode active material tend to increase. Therefore, the effect of improving electrochemical characteristics in a wider temperature range can be easily obtained, which is preferable. The case where the atomic concentration of Ni in the substance is 5 to 25 atomic% is more preferable, and the case where it is 8 to 21 atomic% is particularly preferable.

  The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change with respect to the electrolytic solution. Examples thereof include graphite such as natural graphite (flaky graphite and the like) and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black. Further, graphite and carbon black may be appropriately mixed and used. 1-10 mass% is preferable and, as for the addition amount to the positive mix of a electrically conductive agent, 2-5 mass% is especially preferable.

The positive electrode is composed of a conductive agent such as acetylene black and carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene. Mixing with a binder such as copolymer (NBR), carboxymethyl cellulose (CMC), ethylene propylene diene terpolymer, etc., and adding a high boiling point solvent such as 1-methyl-2-pyrrolidone to knead and mix Then, this positive electrode mixture was applied to a current collector aluminum foil, a stainless steel lath plate, etc., dried and pressure-molded, and then subjected to vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It can be manufactured by heat treatment.
The density of the part except the collector of the positive electrode is usually at 1.5 g / cm ³ or more, for further increasing the capacity of the battery, it is preferably 2 g / cm ³ or more, more preferably, 3 g / cm ³ It is above, More preferably, it is 3.6 g / cm ³ or more. The upper limit is preferably 4 g / cm ³ or less.

Examples of the negative electrode active material for a lithium secondary battery include lithium metal, lithium alloy, and a carbon material capable of occluding and releasing lithium (easily graphitized carbon and a (002) plane spacing of 0.37 nm or more). Non-graphitizable carbon, graphite with (002) plane spacing of 0.34 nm or less, etc.], tin (single), tin compound, silicon (single), silicon compound, lithium titanate such as Li ₄ Ti ₅ O ₁₂ A compound etc. can be used individually by 1 type or in combination of 2 or more types.
Among these, it is more preferable to use a highly crystalline carbon material such as artificial graphite or natural graphite in terms of the ability to occlude and release lithium ions, and the plane spacing (d ₀₀₂ ) of the lattice plane ( ₀₀₂ ) is 0. It is particularly preferable to use a carbon material having a graphite-type crystal structure of 340 nm (nanometer) or less, particularly 0.335 to 0.337 nm.
A mechanical action such as compression force, friction force, shear force, etc. is repeatedly applied to artificial graphite particles having a massive structure in which a plurality of flat graphite fine particles are assembled or bonded non-parallel to each other, for example, scaly natural graphite particles, Using graphite particles that have been subjected to spheroidization treatment, the density of the portion excluding the current collector of the negative electrode can be obtained from X-ray diffraction measurement of the negative electrode sheet when pressed to a density of 1.5 g / cm ³ or more. When the ratio I (110) / I (004) of the peak intensity I (110) of the (110) plane of the graphite crystal and the peak intensity I (004) of the (004) plane is 0.01 or more, the temperature becomes even wider. It is preferable because electrochemical characteristics are improved, more preferably 0.05 or more, and still more preferably 0.1 or more. Moreover, since it may process too much and crystallinity may fall and the discharge capacity of a battery may fall, an upper limit is preferable 0.5 or less, and 0.3 or less is more preferable.
In addition, it is preferable that the highly crystalline carbon material (core material) is coated with a carbon material having lower crystallinity than the core material because electrochemical characteristics in a wide temperature range are further improved. The crystallinity of the coating carbon material can be confirmed by TEM.
When a highly crystalline carbon material is used, the lithium secondary battery according to the present invention tends to react with the non-aqueous electrolyte during charging and lower the electrochemical characteristics in a wide temperature range due to an increase in interface resistance. Then, the electrochemical characteristics in a wide temperature range are good.

  Examples of the metal compound capable of inserting and extracting lithium as the negative electrode active material include Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, and Cu. , Zn, Ag, Mg, Sr, Ba, and other compounds containing at least one metal element. These metal compounds may be used in any form such as a simple substance, an alloy, an oxide, a nitride, a sulfide, a boride, and an alloy with lithium, but any of a simple substance, an alloy, an oxide, and an alloy with lithium. Is preferable because the capacity can be increased. Among these, those containing at least one element selected from Si, Ge and Sn are preferable, and those containing at least one element selected from Si and Sn are particularly preferable because the capacity of the battery can be increased.

The negative electrode is kneaded using the same conductive agent, binder, and high-boiling solvent as in the production of the positive electrode, and then the negative electrode mixture is applied to the copper foil of the current collector. After being dried and pressure-molded, it can be produced by heat treatment under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.
The density of the portion excluding the current collector of the negative electrode is usually 1.1 g / cm ³ or more, and is preferably 1.5 g / cm ³ or more, particularly preferably 1.7 g in order to further increase the capacity of the battery. / Cm ³ or more. The upper limit is preferably 2 g / cm ³ or less.

  Moreover, lithium metal or a lithium alloy is mentioned as a negative electrode active material for lithium primary batteries.

The structure of the lithium battery is not particularly limited, and a coin-type battery, a cylindrical battery, a square battery, a laminated battery, or the like having a single-layer or multi-layer separator can be applied.
Although it does not restrict | limit especially as a battery separator, The monolayer or laminated | stacked microporous film, woven fabric, a nonwoven fabric, etc. of polyolefin, such as a polypropylene and polyethylene, can be used.

  The lithium secondary battery according to the present invention has excellent electrochemical characteristics in a wide temperature range even when the end-of-charge voltage is 4.2 V or more, particularly 4.3 V or more, and the characteristics are also good at 4.4 V or more. is there. The end-of-discharge voltage is usually 2.8 V or more, and further 2.5 V or more, but the lithium secondary battery in the present invention can be 2.0 V or more. Although it does not specifically limit about an electric current value, Usually, it uses in the range of 0.1-30C. Moreover, the lithium battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is -10-80 degreeC.

  In the present invention, as a countermeasure against an increase in the internal pressure of the lithium battery, a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed. Further, as a safety measure for preventing overcharge, the battery lid can be provided with a current interruption mechanism that senses the internal pressure of the battery and interrupts the current.

[Second electrochemical element (electric double layer capacitor)]
The 2nd electrochemical element of this invention is an electrochemical element which stores energy using the electrical double layer capacity | capacitance of electrolyte solution and an electrode interface. An example of the present invention is an electric double layer capacitor. The most typical electrode active material used in this electrochemical device is activated carbon. Double layer capacity increases roughly in proportion to surface area.

[Third electrochemical element]
The third electrochemical element of the present invention is an electrochemical element that stores energy by using electrode doping / dedoping reactions. Examples of the electrode active material used in this electrochemical element include metal oxides such as ruthenium oxide, iridium oxide, tungsten oxide, molybdenum oxide, and copper oxide, and π-conjugated polymers such as polyacene and polythiophene derivatives. Capacitors using these electrode active materials can store energy associated with electrode doping / dedoping reactions.

[Fourth electrochemical element (lithium ion capacitor)]
The 4th electrochemical element of this invention is an electrochemical element which stores energy using the intercalation of the lithium ion to carbon materials, such as a graphite which is a negative electrode. It is called a lithium ion capacitor (LIC). Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, and those using a π-conjugated polymer electrode doping / dedoping reaction. The electrolyte contains at least a lithium salt such as LiPF ₆ .

  Examples of the electrolytic solution of the present invention are shown below, but the present invention is not limited to these examples.

Examples 1-23, Comparative Examples 1-2
[Production of lithium ion secondary battery]
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (the positive electrode active material, the pH of the supernatant liquid when 10 g of the positive electrode active material is dispersed in 100 ml of distilled water is 10.8); 94% by mass, acetylene black ( Conductive agent); 3% by mass is mixed and added to a solution in which polyvinylidene fluoride (binder); 3% by mass is previously dissolved in 1-methyl-2-pyrrolidone. Prepared. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, punched out to a predetermined size, and a positive electrode sheet was produced. The density of the portion excluding the current collector of the positive electrode was 3.6 g / cm ³ . Further, 95% by mass of artificial graphite coated with amorphous carbon (negative electrode active material, d ₀₀₂ = 0.335 nm) and 5% by mass of polyvinylidene fluoride (binder) in advance are added to 1-methyl-2-pyrrolidone. A negative electrode mixture paste was prepared by adding to the dissolved solution and mixing. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried and pressurized, and punched into a predetermined size to produce a negative electrode sheet. The density of the portion excluding the current collector of the negative electrode was 1.5 g / cm ³ . As a result of X-ray diffraction measurement using this electrode sheet, the ratio of the peak intensity I (110) of the (110) plane of the graphite crystal to the peak intensity I (004) of the (004) plane [I (110) / I (004)] was 0.1. And it laminated | stacked in order of the positive electrode sheet, the separator made from a microporous polyethylene film, and the negative electrode sheet, the nonaqueous electrolyte of the composition of Table 1 was added, and the 2032 type coin battery was produced.

[Evaluation of low temperature characteristics after high temperature charge storage]
Initial discharge capacity Using the coin battery produced by the above method, in a constant temperature bath at 25 ° C, charge at a constant current of 1C and a constant voltage for 3 hours to a final voltage of 4.2V. Was discharged to a final voltage of 2.75 V under a constant current of 1 C, and the initial 0 ° C. discharge capacity was determined.
High temperature charge storage test Next, this coin battery was charged in a constant temperature bath at 85 ° C. with a constant current of 1 C and a constant voltage for 3 hours to a final voltage of 4.2 V, and stored for 3 days while being maintained at 4.2 V. It was. Then, it put into the thermostat of 25 degreeC, and discharged once to the final voltage 2.75V under the constant current of 1C.
Discharge capacity after high-temperature charge storage Further, the discharge capacity at 0 ° C. after high-temperature charge storage was determined in the same manner as the measurement of the initial discharge capacity.
Low-temperature characteristics after high-temperature charge storage The low-temperature characteristics after high-temperature charge storage were determined from the following maintenance rate of 0 ° C. discharge capacity.
0 ° C. discharge capacity retention rate after storage at high temperature (%) = (0 ° C. discharge capacity after high temperature storage / initial 0 ° C. discharge capacity) × 100
In addition, Table 1 shows battery manufacturing conditions and battery characteristics.

Examples 24 to 25, Comparative Example 3
Instead of the negative electrode active material used in Example 2, Example 18, and Comparative Example 1, a negative electrode sheet was prepared using silicon (single element) (negative electrode active material). Silicon (simple substance); 80% by mass, acetylene black (conductive agent); 15% by mass were mixed, and polyvinylidene fluoride (binder); 5% by mass was previously dissolved in 1-methyl-2-pyrrolidone. In addition to the solution, mixing was performed to prepare a negative electrode mixture paste. Except that this negative electrode mixture paste was applied onto a copper foil (current collector), dried and pressurized, punched out to a predetermined size, and a negative electrode sheet was produced, Example 2, Example 18, A coin battery was produced in the same manner as in Comparative Example 1, and the battery was evaluated. The results are shown in Table 2.

Examples 26 to 27, Comparative Example 4
A positive electrode sheet was produced using LiFePO ₄ (positive electrode active material) coated with amorphous carbon instead of the positive electrode active material used in Example 2, Example 18, and Comparative Example 1. LiFePO ₄ coated with amorphous carbon; 90% by mass, acetylene black (conducting agent); 5% by mass are mixed in advance, and polyvinylidene fluoride (binder); 5% by mass is added to 1-methyl-2-pyrrolidone. The positive electrode mixture paste was prepared by adding to and mixing with the solution previously dissolved in the mixture. This positive electrode mixture paste was applied onto an aluminum foil (current collector), dried, pressurized and punched to a predetermined size to produce a positive electrode sheet, and the end-of-charge voltage during battery evaluation was 3. A coin battery was fabricated and evaluated in the same manner as in Example 2, Example 18, and Comparative Example 1 except that the voltage was 6 V and the discharge end voltage was 2.0 V. The results are shown in Table 3.

Any of the lithium secondary batteries of Examples 1 to 10 described above includes a branched dinitrile compound in which the main chain of the alkylene chain connecting two nitrile groups in the nonaqueous electrolytic solution of the present invention has 2 to 4 carbon atoms. Comparison of the lithium secondary battery of Comparative Example 1 in the case where the nitrile group is not present and the case where the main chain of the alkylene chain linking the two nitrile groups is replaced with a branched dinitrile compound having 2 to 4 carbon atoms and a linear dinitrile compound is included. Compared with the lithium secondary battery of Example 2, the electrochemical characteristics in a wide temperature range are remarkably improved.
The lithium secondary batteries of Examples 11 to 23 are all branched dinitrile compounds in which the main chain of the alkylene chain connecting two nitrile groups in the nonaqueous electrolytic solution of the present invention has 2 to 4 carbon atoms. And Comparative Example 1 in which the alkylene chain connecting the two nitrile groups does not contain a linear dinitrile compound having 2 to 6 carbon atoms, Comparative Example 2 in the case of containing only a linear dinitrile compound Compared with the battery, the electrochemical characteristics in a wide temperature range are remarkably improved. As described above, the effect of the present invention is that the main chain of the alkylene chain connecting the two nitrile groups of the present invention has 2 to 4 carbon atoms in the nonaqueous electrolytic solution in which the electrolyte salt is dissolved in the nonaqueous solvent. When the branched dinitrile compound is contained in an amount of 0.001 to 5% by mass and the non-aqueous solvent contains a cyclic carbonate having a fluorine atom in an amount of 0.1 to 30% by volume, or an alkylene linking two nitrile groups It has been found that the effect is unique when the chain contains 0.001 to 5% by mass of a linear dinitrile compound having 2 to 6 carbon atoms.
In addition, from the comparison between Examples 24 to 25 and Comparative Example 3, from the case of using silicon (simple substance) for the negative electrode, or from the comparison between Examples 26 to 27 and Comparative Example 4, the lithium-containing olivine-type iron phosphate salt to the positive electrode The same effect can be seen when using. Therefore, it is clear that the effect of the present invention is not an effect dependent on a specific positive electrode or negative electrode.

  Furthermore, the non-aqueous electrolyte of the present invention also has an effect of improving the discharge characteristics in a wide temperature range of the lithium primary battery.

  If the non-aqueous electrolyte of the present invention is used, an electrochemical element having excellent electrochemical characteristics over a wide temperature range can be obtained. Especially when used as a non-aqueous electrolyte for electrochemical devices mounted on hybrid electric vehicles, plug-in hybrid electric vehicles, battery electric vehicles, etc., electrochemical devices that do not easily deteriorate in electrochemical characteristics over a wide temperature range Can be obtained.

Claims (8)

In a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous solvent contains 0.1 to 30% by volume of a cyclic carbonate having a fluorine atom, and two nitrile groups are further contained in the nonaqueous electrolytic solution. A non-aqueous electrolyte for a lithium battery or a lithium ion capacitor , wherein a branched dinitrile compound having a main chain of an alkylene chain to be linked having 2 to 4 carbon atoms is contained in an amount of 0.001 to 5% by mass. In a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, a branched dinitrile compound in which the main chain of an alkylene chain connecting two nitrile groups in the non-aqueous electrolyte solution has 2 to 4 carbon atoms is 0 0.001 to 5% by mass of a lithium battery containing 0.001 to 5% by mass of a linear dinitrile compound containing 2 to 6 carbon atoms in an alkylene chain connecting two nitrile groups Or a non-aqueous electrolyte for a lithium ion capacitor . In a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous solvent contains 0.1 to 30% by volume of a cyclic carbonate having a fluorine atom, and two nitrile groups are further contained in the nonaqueous electrolytic solution. 0.001 to 5% by mass of a branched dinitrile compound in which the main chain of the alkylene chain to be linked has 2 to 4 carbon atoms, and an alkylene chain to link the two nitrile groups are 2 to 6 carbon atoms A non-aqueous electrolyte for a lithium battery or a lithium ion capacitor , comprising 0.001 to 5% by mass of a chain dinitrile compound. As the linear dinitrile compound, one having a different number of carbon atoms from the alkylene chain connecting the two nitrile groups constituting the linear dinitrile compound than the main chain carbon number of the branched dinitrile compound is used. The non-aqueous electrolyte for a lithium ion battery or a lithium ion capacitor according to claim 2 or 3. 5. The branched dinitrile compound according to claim 1, wherein at least one hydrogen atom of the main alkylene chain is substituted with an alkyl group having 1 to 2 carbon atoms. Nonaqueous electrolyte for lithium batteries or lithium ion capacitors . 6. The branched dinitrile compound according to claim 5, wherein, of the two nitrile groups, only one hydrogen atom bonded to the α-position carbon of one nitrile group is substituted with a methyl group. Nonaqueous electrolyte for lithium batteries or lithium ion capacitors . The branched dinitrile compound is 2-methylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2-ethyl-3-methylsuccinonitrile, 2,2,3-trimethylsuccinonitrile, 2-methylglutaro Nitrile, 2,4-dimethylglutaronitrile, 2-ethyl-4-methylglutaronitrile, 2,2,4-trimethylglutaronitrile, 2,3-dimethylglutaronitrile, 2,3,4-trimethylglu Talonitrile, 2-methyladiponitrile, 2,5-dimethyladiponitrile, 2-ethyl-5-methyladiponitrile, 2,2,5-trimethyladiponitrile, 2,3-dimethyladiponitrile, 2. At least one selected from 2,4-dimethyladiponitrile and 2,3,5-trimethyladiponitrile Non-aqueous electrolyte for a lithium battery or a lithium ion capacitor according to. The positive electrode, according to any the electrochemical device is a negative electrode and a nonaqueous lithium battery or a lithium ion capacitor electrolyte salt with a non-aqueous electrolyte solution that is dissolved in a solvent, the nonaqueous electrolytic solution of claim 1-7 A non-aqueous electrolyte for a lithium battery or a lithium ion capacitor .